On a nationwide basis, the incidence of trench cave-ins has been a news item that appears with disturbing regularity. Even with the inclusion of retaining walls and associated supports, the devices according to the prior art are generally difficult to assemble and therefore time consuming in their deployment, or else they are more easily deployed but do not provide adequate protection for the workmen within the environment. Since a common activity when working in trenches is the laying of pipe and the like, heavy hoisting equipment is usually present in order to allow the piping to be inserted within the trench. Prior art devices which appear to most closely approximate the instant invention include the following patents, but do not appear to benefit from the presence of on site hoisting equipment:
U.S. Pat. No. 3,114,244 Silver; U.S. Pat. No. 3,316,721 Heilig; PA1 U.S. Pat. No. 3,254,490, Moore; U.S. Pat. No. 3,869,868 Irsai.
Each of these references teaches the use of a retaining wall support device which cannot be conveniently advanced along the length of the trench as does the instant application, and therefore any similarities between these devices and the instant application are merely coincidental.